We have done preliminary characterization of mitochondrial DNAs isolated from three species of Drosophila. Electron microscope heteroduplex and restriction endonuclease analyses have revealed that these mtDNAs have undergone a significant evolutionary divergence in their nucleotide sequences. We are constructing specific cleavage maps of these mtDNAs using various restriction endonucleases. Restriction endonucleases recognize specific base sequences within a DNA molecule and have proven useful in mapping genes and detecting single base-pair substitutions. Utilizing this information, our objectives are to understand (1) organization of genes as related to function, (2) how the gene arrangements change, (3) the rates of evolution of small DNAs, and (4) heterogeneity of intraspecific mtDNA.